COSINE RESPONSE CHARACTERISTICS OF SOME RADIOMETRIC AND PHOTOMETRIC SENSORS

Global and diffuse irradiance and illuminance are measured with instruments that are assumed to have true cosine responses. From one refereed paper, some institutional reports, and by word-of-mouth, it is generally known that no instrument is perfect in this regard. This paper reports on measurements of cosine responses for several commercial instruments and on the cosine response of a multi-filter rotating shadowband radiometer. The measurements were made with an automated cosine response test bench using the same protocol for each instrument. The cosine bench measures with variable angular resolution as fine as 0.25-degrees. The automated rotation is in one plane. A manual rotation allows measurements at other azimuths.